Experiment 4
We have done some experiments with cells and batteries and our bulb, now let's add bulbs to our work.
STEP 1. Cut two more bulbs out of the string. This time don't bother to separate them. Keep them in series. Now you will have one single bulb and two in series.
STEP 2. Connect two cells in series so you will have 3 volts to work with. Test the two cells on a single bulb and note the brightness.
STEP 3. Now use two bulbs in series. Test the brightness.
You can see in these last two photos that the series bulbs are dimmer.
STEP 4. Now add a bulb to your series. Test the brightness. They barely glow in my example!
DISCUSSION. When we add bulbs in series the electricity is divided between the bulbs. With one bulb in the system, all 3 Volts are applied and the bulb burns brightly. But, when we have two, then each bulb gets only 1.5 volts. They are dim just like they were attached to one cell. If we have three in the series the 3 volts is divided into 3, so each bulb only receives 1 volt.
STEP 5. Try your three lights in a series with a 9 volt battery.
They all should light nicely.
STEP 6. What happens if one of the wires is loose? What happens if you pull a bulb out of its socket/holder? Does the string stay on or go off?
Discussion. Christmas tree lights often go bad because one bulb is burned out. Many circuits in series so that if any part is not making a connection, the whole string is dead.
Consider that most series strings of these bulbs consist of about 50 individual bulbs. We plug them into our home electrical supplies that average 120 volts. So how many volts does each bulb "see?"
120 Volts/50 bulbs = 2.4 Volts per light.
This is just enough voltage to make each bulb light brightly.
Challenge: Let's suppose you want to put Christmas lights on your car. An automotive battery is 12 volts. What number of bulbs could you string together in series to light them brightly? Do the experiment! Cut out the number of bulbs in the string that you have calculated and get someone to help you connect it to the car battery!
RETURN TO 10 EXPERIMENTS WITH A DEAD STRING OF CHRISTMAS LIGHTS